An in vivo and in vitro Study of the Loss of Plasticizer from Soft Polymer-gel Materials

Abstract

Polymer-gel materials used as short-term denture soft linings are blended with plasticizers to lower the glass transition temperature (Tg). A lower Tg allows for greater polymer chain mobility, thus producing a more flexible material. The present work evaluated the loss of plasticizers due to leaching both in vivo and in vitro. Two commercial denture soft-lining materials (A and B) were tested. These were both poly(ethyl methacrylate) polymers, blended with alcohol and phthalate esters. A clinical study was conducted in which patients wore, sequentially, dentures bearing (on separate occasions) each of the two soft-polymer lining materials. The two materials A and B were randomly assigned for each of ten patients and were worn for 14 and 30 days, respectively. With one exception, patients wore dentures with both lining materials, for a total of 19 clinical evaluations. The plasticizer loss occurring during the clinical trial was determined by GC analysis from the initial and terminal day sampling of plasticizer content of the soft polymer-gel materials. The results of this analysis were compared with results obtained from an in vitro leachability study by use of sink conditions in water at 37 degrees C for the same two commercial soft polymers conducted over the same time periods of 14 and 30 days. The results indicated that a higher loss of plasticizer occurred in vivo, compared with the in vitro tests for 17 of the 19 clinical evaluations. The average plasticizer lost in vivo from material A at 14 days was 122 +/- 58 mg/g, and for material B at 30 days it was 33 +/- 27 mg/g.(ABSTRACT TRUNCATED AT 250 WORDS)

The dynamic viscoelasticity and water absorption characteristics of soft acrylic resin materials containing adipates and a maleate plasticizer

“…Several investigators have reported on the leachability of plasticizers from soft dental polymers 6,9,32) . The loss of viscoelasticity in tissue conditioners in clinical use may be due to the leaching out of the plasticizer from the soft polymer gel material, accompanied by water absorption.…”

Histopathological Changes by the Use of Soft Reline Materials: A Rat Model Study

“…Since the increase of the thickness of the oral mucosa under the denture base is also considered a physiological response to mechanical loading [47]–[52], and no compressive forces was reproduced in this study because the plates were fixed in the molars, we may not expect any increased proliferative activity of the epithelial cells due the mechanical compression factors [49]–[52]. The histopathological changes assessed may be a response of the epithelium to the release of toxic substances [20]–[21], [26], [41], [52]–[54] and/or residual monomers [24], [31]. Despite the cytotoxicity reported in vitro [26], in this present in vivo study no histopathological changes of the epithelium were observed forlining resins tested without the application of post-polymerization heat treatment.…”

“…Free radical polymerization reaction does not result in complete conversion of all carbon–carbon double bonds and therefore, acrylic resins are known to contain and release unpolymerized monomers [7], [20]. The leachability of plasticizers (such as phthalates) released in water [21]–[22] and residual monomer may also induce a direct cytotoxic effect on cells [23]–[26]. Toxic compounds may be released into the patient's mouth during the polymerization of soft reline materials in contact with the oral mucosa in the relining procedure.…”

Effect of PMMA polymer on the dynamic viscoelasticity and plasticizer leachability of PEMA-based tissue conditioners

“…The present study did not completely simulate clinical behavior because viscoelasticity specimens were tested in the dry state, and all specimens were immersed in distilled water. Several investigators have reported that the plasticizer loss was higher in vivo than in vitro 13,32) . To overcome the limitations of the in vitro tests, the viscoelasticity of tissue conditioners actually used by patients should be evaluated; and artificial saliva should be used as an immersion solution.…”

“…Several investigators have reported on the leachability of plasticizers from soft dental polymers 9,13,32) . The loss of viscoelasticity of tissue conditioners in clinical use may be due to the leaching out of the plasticizer from the soft polymer gel material.…”